Herscher Anticline (New Name)
Old Name: Herscher Dome
Location
T30N, R10E, Kankakee County (C-7)
References
D.J. Fisher (unpublished) cited in Athy 1928, Willman and Templeton 1951, Bell 1961, Buschbach 1964, Bristol and Buschbach 1973, Buschbach and Bond 1967, 1974
Description
Interpreting borehole data and outcrops of Silurian strata along the Kankakee River, Fisher (cited in Athy 1928} identified a north-trending anticline, which he called the Ritchey-Herscher arch, in the Herscher area. Subsequent researchers referred to this structure as the Herscher Anticline or Dome. The name Herscher Anticline is used in this report because the fold is elongated and has a well defined axis. The Herscher Anticline trends north to north-northwest. It was delineated by drilling for a gas storage field in the Cambrian Galesville and Mt. Simon Sandstones.
The Galena (Trenton) Group structure map of Bristol and Buschbach (1973) shows the Herscher Anticline is a southward- plunging, asymmetrical anticline that has a steeper west flank and is a part of the La Salle Anticlinorium. The long axis of the anticline can be traced for approximately 18 miles (29 km). The top of the Mt. Simon Sandstone has closure of approximately 90 feet (27 m); the area of closure has a width of slightly more than 2 miles (3.2 km) and a length, trending north-northwest, of slightly more than 6 miles (10 km). A saddle, perpendicular to the long axis and dropping to approximately 40 feet (12 m) above the closure elevation, divides the anticline into a northern dome covering about one-third of the total area of closure and a southern anticline covering about two-thirds. Three smaller areas of closure, the Herscher-Northwest Anticline and two unnamed domes, lie northwest of the Herscher Anticline (Bristol and Buschbach 1973). Gas is stored in the Elmhurst Sandstone Member of the Eau Claire Formation at Herscher and in the Mt. Simon Sandstone, as well as the substantially thinner Elmhurst Member at Herscher-Northwest.
The Herscher Anticline is rather unusual among anticlines along the La Salle Anticlinorium in that the amount of closure decreases with depth. Closure decreases from about 200 feet (60 m) on the Galena to 100 feet (30 m) on the Galesville and 80 feet (24 m) on the Mt. Simon. Downward loss of closure has been attributed to northward thinning of most beds (Buschbach and Bond 1967, 1974). No well on or near Herscher Dome has reached Precambrian rock, and no evidence of its basement configuration is available.
The Herscher Anticline may have developed concurrently with the La Salle Anticlinorium, but direct proof is unavailable because the La Salle structures are post-Mississippian, and no rock younger than Silurian is preserved on or near the Herscher Anticline.
References
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